AGL
Pronunciation: A-G-L (spelled out)
Also written as: AGL — Above Ground Level
Above Ground Level — a measurement of altitude or height expressed relative to the terrain directly beneath the aircraft, rather than sea level.
Full Definition
AGL (Above Ground Level) is a standard aviation measurement used to express an aircraft's height above the actual ground surface below it, in contrast to MSL (Mean Sea Level), which measures altitude from a fixed datum. In airside operations, AGL measurements are critical for obstacle clearance calculations, approach minima, and lighting system specifications. Editors working on approach procedures, obstacle assessments, or aerodrome design documents must ensure AGL and MSL values are not transposed. The abbreviation is always rendered in full capitals without periods.
Usage
Usage note: Always expressed in feet (ft) in ICAO documents unless metres are specifically required. Do not conflate with MSL, which is measured from sea level. Both values may appear in the same sentence and must be explicitly labelled.
In Context
- "The obstacle penetrates the Obstacle Limitation Surface at 52 ft AGL." — Aerodrome Obstacle Assessment Report
- "Decision altitude is expressed in feet MSL, whereas obstacle clearance heights are given in feet AGL." — Instrument Approach Procedure Design Document